The invention relates generally to semiconductor transducers and, more particularly, to such transducer assemblies that employ a single block semiconductor carrier structure for supporting semiconductor piezoresistive elements (e.g., strain gages).
Semiconductive transducers are widely used in automotive, biomedical and a variety of other applications because of their relatively small dimensions, reliability and high signal output relative to other devices. In performing the transducer function, one or more piezoresistive semiconductor elements are utilized, in which the resistance thereof varies according to the intensity or magnitude of an applied force upon an associated diaphragm to which the elements are mechanically coupled (bonded). The diaphragm to which the force is applied is typically a metal or semiconductor membrane-like substrate upon which the piezoresistive elements are dielectrically mounted. A force applied to the diaphragm deflects the diaphragm and hence causes the associated piezoresistive element to vary resistance in accordance with the deflection. The force being measured is transferred to the piezoresistive element, which is strain responsive, causing the element to expand or compress, thereby producing a change in the electrical resistance of the element. The piezoresistive elements are typically arranged in a Wheatstone bridge circuit with one to four of the bridge legs being active. Other circuit configurations are also possible.
A desire is to continue improving the characteristics of transducers of the foregoing type so that devices may be manufactured that are relatively small, sensitive and which produce a relatively large resistance in a relatively small area. The devices should also exhibit a linear operation and small deviations in sensitivity and null offset over a wide range of temperatures, as well as having a relatively low manufacturing cost.
A problem in achieving these improved characteristics and cost efficiencies, however, relates to the manner in which prior art transducers are manufactured and assembled. Prior art transducer assemblies require multiple piezoelectric elements, i.e., "gages," to be manufactured as discrete elements. Manufacturing process and material variations contribute to a lack of uniformity of these elements. The gages must subsequently be electrically normalized based upon their mechanical deviation and their deviation from optimum bonding position on the diaphragm, and it is therefore difficult to achieve consistent results from one transducer assembly to the next.